Nonblocking electrolytic recording medium

ABSTRACT

A nonblocking electrolytic recording medium is disclosed. The medium includes a base sheet of absorbent paper impregnated at a level of at least 40 percent by weight of moisture with an electrolytically conducting marking solution. The solution contains an aqueous dispersible liquid silicone, preferably 0.005 to 2.0 grams per 100 milliliters of a polymethyl-siloxane having a viscosity at 25* C. between about 10 to about 100 centistokes.

United States Patent inventor Arthur W. Sperling Amityville, N.Y.

June 4, 1968 Jan. 4, 1972 Hogan Faximlle Corporation Los Angeles, Calif.

Appl. No. Filed Patented Assignee NONBLOCKING ELECTROLYTIC RECORDINGMEDIUM 9Claims,NoDrawings U.S.(l 117/201, 117/161ZA,204/2,117/155 UA1nt.C1 B44d1/02 FieldofSearch 117/201,

155 V, 161 ZA; 204/2; 346/74 [56] References Cited UNITED STATES PATENTS3,335,221 8/ 1 967 Barnes et a1. 346/74 X 3,123,542 3/1964 Mandel et al.204/2 3,342,704 9/ 1967 Gradsten et al.. 204/2 3,344,043 9/1967 Lieblichet a1. 204/2 3,459,593 8/1969 Cole 117/155 V X Primary Examiner-AlfredL. Leavitt Assistant ExaminerCaleb Weston Attorneys-Samuel Lindenbergand Arthur Freilich NONBLOCKING ELECTROLYTIC RECORDING MEDIUM BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates toelectrosensitive recording media and more particularly to an improved,nonblocking recording medium.

2. Description of the Prior Art An electrolytic recording medium of thetype utilized in facsimile recorders is prepared by impregnating anabsorbent base sheet with an electrolytically conducting solutioncontaining a marking compound. In the recorder that is now in generaluse, marking is effected by disposing the impregnated paper between astationary blade anode electrode and a cooperating rotating helicalcathode. When a voltage is applied between the electrodes, current flowsthrough the paper at the moving intersection of the electrodes. Metalions supplied by electrolytic dissolution of the anode react with themarking compound to form a colored mark onthe surface of the paperwherever the anode contacts the paper adjacent the oppositely disposedcathode.

Large volumes of this paper are consumed in the facsimilerecordingmachines utilized by the wire services. Continuous production of exactcopy is imperative and, therefore, the paper must satisfy several veryimportant specifications. The paper must have the ability to producemarks having a density which is a function, preferably linear, of thecurrent passed through the paper. The marking compound must producecolor tones varying uniformly through a range from white at zero currentflow through grays for intermediate magnitudes of current to black forthe highest or maximum current magnitudes. There should be a minimum ofbleeding or fringing of the mark so as to maintain a sharply detailedand defined recorded image.

The wet paper is stored at high humidity in special containers forextended periods prior to use in a recorder and must remain stablewithout chemical decomposition or loss of ingredients which would causediscoloration of the paper before use or background discoloration afterbeing recorded. It is also desirable to employ a paper that isinsensitive to light even after exposure to ultraviolet light as inOzalid duplicating machines.

In many of the present electrolytic recording papers, apolyhydroxyphenolic such as catechol has a tendency to diffuse ortransfer out of the paper and discolor adjacent sheets of paper andother surfaces such as the recorder cabinet and walls of the roomcontaining the recorder.

Moreover, bearing in mind that wire service facsimile machines are inalmost continuous use, it is not uncommon to encounter a condition inwhich current flow through the electrodes is hindered or blocked by theaccumulation of fibers or precipitated salts on the helical blade. Theimpedance to current flow phenomena at these points has been commonlyreferred to as blocking. When current is blocked, no mark can be formeduntil the materials are dislodged from that portion of the blade.Moreover, the salting out or precipitation of the materials present inthe impregnant may result in a discoloration of the background of thesheet.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of theinvention to provide an improved electrosensitive graphic recordingmedia.

Another object of the invention is the provision of an improvednonblocking electrolytic recording medium.

Another object of the invention is to provide a nonblockingelectrosensitive recording medium which contains a nontransferringmarking ingredient and which is not susceptible to backgrounddiscoloration before and after recording.

Other objects and many attendant advantages of the invention will becomeapparent to those skilled in the art as the description proceeds.

In accordance with the invention, it has beendiscovered that anonblocking stable, electrosensitive recording medium is prepared byimpregnating a porous support with an aqueous solution containing amark-forming compound. an electrolyte and a water-dispersible. organicsilicone polymer. The electrosensitive recording medium of the inventiondoes not result in any blocking even after being run for considerableperiods through the same facsimile-recording apparatus. The paper isstable to light and does not discolor either before or after recordingand the marks that are formed are clear and distinct.

The invention will become better understoodby reference to the followingdetailed description.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance withthepresent invention, the water-dispersible, organic silicone polymer ispreferably a linear organic polysiloxane of the formula:

l S B where R is preferably lower alkyl such as methyl or ethyl, but

can also be aryl such as phenyl or hydroxy, amino, lower alkenyl orlower alkoxy, and n is an integer between 0 and 2,000. The polymer is anoily liquid exhibiting a viscosity which can be varied within widelimits, but preferably is from about 5 to 500 centistokes (cs.) at 25 C.and most suitably from 10 to cs. Polydimethylsiloxanes in amounts fromabout 0.005 to 2.0 grams per 100 milliliters of water are found todisperse readily to form electrolytic recording media.

The marking agents are typically polyhydroxyaromatic compounds in whichat least two of the phenolic hydroxyl groups are ortho to each other.The aryl ring nucleus may be substituted with various othersubstitutents to vary certain properties such as vapor pressure andstability. Such compounds may be selected from those of the followinggeneral formula:

where R"' R"' and R are lower alkyl, amino, lower alkoxy, aryloxy, carbxy, sulfoxy, hydroxy, lower alkanoyl, lower alkenoyl, haloror hydrogen.R is R or R X where X is carboxy or sulfoxy, and R" is -(CR'R"),, or--NH-(CRR),. where n is an integer from 1 to ID, and R and R" arehydrogen, hydroxyl, amino or lower alkyl. The (CRR")-- group may beunsaturated. Condensed nuclear aromatic compounds may also be used asmarking compounds. For example, hydroxynaphthalene compounds such ashydroxynaphthoic acid is a suitable marking compound. Other examples ofmarking compounds are gallic acid, catechol, pyrogallol, gentisic acid,chromotropic acid, protacatechuic acid, caffeic acid and adihydroxyphenyl alkanoic acid such as 3, 4- dihydroxyphenylacetic acid(DHPAA).

DHPAA and analogous compounds are advantageous in that the capability oftransferring from the paper is substantially reduced. However, atconcentrations desired for optimum electrolytic marking, DHPAA is poorlysoluble in the media and tends to crystallize out further aggravatingthe blocking phenomena previously discussed. The water-dispersiblesilicone-containing formulations of the invention are par ticularlyeffective in eliminating the blocking of electrolytic recording mediacontaining poorly soluble compounds such as DHPAA. This class ofcompounds is represented by compounds of the general formula:

where R", R. and R may be lower alkyl, amino, lower alkoxy, hydroxy,lower alkanoyl, halo, or hydrogen. R may be an alkylene oramino-alkylene moiety of the formula -(CRR)- or NH(CR"R),. where n is aninteger from 1 to 10, and R or R" may be H, lower alkyl, amino, hydroxyor other suitable substituents. X is COOH or S H. Examples of othersuitable marking compounds within this class are 3, 4-dihydroxybetaphenylpropionic acid (DHPPA) and 3, 4-dihydroxyaniline-N-methyl-sulfonic acid( DHAMSA).

The recording medium generally comprises an absorbant, inert, porous andpreferably white support such as a sheet of paper having a high wetstrength which is impregnated with an aqueous solution of anelectrolytic recording impregnant. The impregnant contains the markingcompound, an electrolyte and usually, also a stabilizer, an acidifierand one or more antifringing agents.

Recording paper is prepared by passing the porous sheet through a bathof impregnant. Approximately 2.5 to 3.0 cc. of the solution is requiredper square foot of paper in a typical case. The solution is permitted todistribute itself throughout the paper. Excess impregnant is removed bypassing the paper through pressure rolls until at least about 40 percentmoisture by weight remains. in order to retard evaporation, therecording paper is generally stored in sealed containers until neededfor recording.

A typical formulation with which recording paper may be impregnated isnow given by way of illustration.

EXAMPLE 1 About 0.4 grams of Dow Corning 200, a polydimethylsilox anehaving a viscosity of 100 centistokes at C. was dispersed into 100 ml.of water. The following ingredients were then added with stirring.

NaCl l4.6 g. NaClO; 4.0 g. DHPAA 2.75 g. Thiourea 0.5 g. Oxalic acid0.0875 g. Monosodium Phosphate (H g.

The solution of example I was filtered and it was observed that thesilicone oil did not separate out. The solution was then permitted tostand overnight and again, no separation of the silicone oil wasevidenced.

A control impregnant was prepared having the identical compositionexcept that the silicone was not present.

A series of hand sheets were impregnated with the solution of example 1and the control impregnant. The papers were hung side by side in awindow to expose them to sunlight. The hand sheet of example 1 was foundto be less affected by ultraviolet light.

The quantity of DHPAA may be varied up to the solubility limit thereofwhich is approximately 40 grams per 100 cc. of solution. The sodiumchloride electrolyte may be replaced with another group I or group IImetal chloride, bromide or nitrate. The chlorides and bromides arepreferred since papers made with nitrates exhibit substantially morediscoloration when exposed to ultraviolet light. Sodium chloride may bepresent in quantities varying from zero to its solubility limit at aboutgrams per 100 cc. of solution and the exact quantity depends upon thedegree of electrical conductivity desired.

Thiourea functions as a stabilizer in the composition of the inventionand may be replaced by other compounds such as lower alkyl derivativesof thiourea or dithiobiuret. The thiourea may be varied from about 6.!grams which is the limit for stability to about 10 grams per cc. ofsolution which is the approximate solubility limit.

The pH of the paper is preferably maintained in the range of from about1.0 to 3.5 by addition of an acid such as oxalic and a buffer such asmonosodium phosphate. At a pH value about 3.5, the mark is apt to changecolor and at a pH of less than i, the mark is generally of lighterdensity than acceptable.

The monosodium phosphate also provides an antifringing function. It maybe present in amounts ranging up to about 0.5 grams above which it tendsto decrease the density of the mark. The sodium chlorate producesadditional marking density by oxidizing the metal ions to a highervalancy state and is also believed to increase the density of the markby polymerization, especially when the recording is heated after themark has formed. DHPPA gives marks of excellent density when used inconjunction with oxidizing agents such as sodium chlorate.

During the recording process, a recorder is employed in which anelectric current is passed through the recording paper while it issandwiched between a rotating helical cathode and a stationary bar anodewhich are in contact with opposite surfaces of the paper. The anode maybe composed of iron, stainless steel, silver or some other eroding metalcapable of electrolytic dissolution to form ions which react with themarking compound to form one or more colored complex compounds whichconstitute the recorded colored marks. The recorded paper may then bedried in air or by some heating device to permanently fix the recordedmarks. The formulations of example 1 and the control were impregnatedinto wet strength paper and the moisture content adjusted to 40 percent.A new stainless steel printer blade was inserted into a recorder and thehelix thoroughly cleaned. Comparison runs of 108 inches of 8.5 inch widepaper were run through the recorder. Copy was run white at no current,then black at maximum current density. Upon the completion of each run,the helix was examined closely for pickup. With the control paper, afterapproximately 25 feet of no current and then maximum marking current,accumulation of material on the helix occurred with blocking of thecurrent and blank spots on the record. With the paper impregnated withthe solution of example I, the recorder ran smoothly throughout thecomplete run. A thin layer of nonoily black material was observed tohave gathered on the blade. This material was easily removable. Thematerial collected only on the side of the blade which was in contactwith the helix through the paper. Production run rolls of paper wereprepared and recorded in a standard wire service recorder underin-service conditions. No blocking effect was observed after several400- foot rolls of paper had been run between the helix and the blade.

it is understood that only preferred embodiments of the invention havebeen disclosed and that numerous substitutions, alterations andmodifications are all permissible without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:

1. An electrolytic recording medium comprising:

an impregnated sheet containing;

an aqueous electrolytically conducting solution at a level of at least40 percent by weight of moisture;

said solution including a polyhydroxy-aromatic marking compound; and

an even dispersion of an aqueous dispersible, liquid, organicpolysiloxane polymer having a viscosity at 25 C. of from 5 to 500 cs.and being present in said solution in an amount of 0.005 to 2.0 gramsper [00 ml. of water.

2. A medium according to claim I in which the polysiloxane has aviscosity at 25 C. of from about l0 to 100 centistokes.

3. A medium according to claim 2 in which the polysiloxane is selectedfrom polymers of the formula:

R R R where R", R and R are lower alkyl, amino, lower alkoxy, loweralkanoyl, halo or hydrogen; and

R" is R or R"X where R" is lower alkylene or aminoalkylene and X iscarboxyl or sulfoxyl. 7. A medium according to claim 6 in which themarking compound is a dihydroxyphenyl alkanoic acid.

8. A medium according to claim 7 in which the marking compound isdihydroxy phenylacetic acid.

9. An electrolytic recording medium comprising: a sheet of paperimpregnated with an aqueous solution at a level of at least 40 percentby weight of moisture; said solution containing on a basis of ml. ofwater; 0.005 to 2.0 grams of a liquid polymethylsiloxane; having aviscosity of from 10 to 100 cs. up to 30 grams of a group I or group llmetal chloride, bromide or nitrate; 0.1 to 5 grams of a thioureacompound; up to 0.5 grams of monosodium phosphate; and up to 40 grams ofdihydroxy phenylacetic acid.

W -h 4. .er.

2. A medium according to claim 1 in which the polysiloxane has aviscosity at 25* C. of from about 10 to 100 centistokes.
 3. A mediumaccording to claim 2 in which the polysiloxane is selected from polymersof the formula: where R is lower alkyl, aryl, hydroxy, amino, loweralkenyl or lower alkoxy and n is an integer from 0 to 2,000.
 4. A mediumaccording to claim 3 in which R is methyl.
 5. A medium according toclaim 1 in which the marking compound is a polyhydroxy-aromatic compoundcontaining at least two phenolic hydroxyl groups which are ortho to eachother.
 6. A medium according to claim 5 in which the marking compound isselected from those of the formula: where Ra, Rb and Rc are lower alkyl,amino, lower alkoxy, lower alkanoyl, halo or hydrogen; and Rd is Ra orReX where Re is lower alkylene or aminoalkylene and X is carboxyl orsulfoxyl.
 7. A medium according to claim 6 in which the marking compoundis a dihydroxyphenyl alkanoic acid.
 8. A medium according to claim 7 inwhich the marking compound is dihydroxy phenylacetic acid.
 9. Anelectrolytic recording medium comprising: a sheet of paper impregnatedwith an aqueous solution at a level of at least 40 percent by weight ofmoisture; said solution containing on a basis of 100 ml. of water; 0.005to 2.0 grams of a liquid polymethylsiloxane having a viscosity of from10 to 100 cs.; up to 30 grams of a group I or group II metal chloride,bromide or nitrate; 0.1 to 5 grams of a thiourea compound; up to 0.5grams of monosodium phosphate; and up to 40 grams of dihydroxyphenylacetic acid.